1. Field of the Invention
This invention relates to a belt transmission device transmitting engine power of a motorcar to an auxiliary apparatus thereof, and more particularly an improvement in reducing tension speed variations of a friction transmission belt having a so-called wedge effect, such as a V-belt, a V-ribbed belt, and the like.
2. Description of the Prior Art
Generally, in an engine of a motorcar, an auxiliary apparatus such as a water pump, an alternator, and the like is drive by engine power through a belt transmission device. This belt transmission device is provided with a driving pulley mounted on a crankshaft of the engine, a driven pulley mounted on a driving shaft of the auxiliary apparatus, and a V-belt trained between both pulleys, arranged so that the engine power is transmitted to the auxiliary apparatus through the V-belt to drive it.
In the belt transmission device in the engine of the motorcar, there is a problem in that belt life is extremely lowered due to tension variations of the V-belt caused by rotational speed variations of the engine. Particularly in a Diesel engine, large torsion vibrations and displacements in rotation occur at the crankshaft, since the compression ratio of the Diesel engine piston is comparatively larger than that of a gasoline engine. And more particularly, while rotational speed variations are comparatively small in a Diesel engine equipped with a manual speed-shifting gear, owing to a large flywheel, in a Diesel engine equipped with an automatic speed-shifting gear the rotational speed variations can hardly be regulated, since a small flywheel is employed therein. Therefore, large tension variations occur in the V-belt due to these large rotational speed variations. The rotational speed variations are increased especially in a low rotational speed range (650 rpm-1000 rpm), with the result that the life of the V-belt is extremely lowered by an inertia load caused by these rotational speed variations.
In order to decrease the tension variations of the V-belt, a tension pulley is conventionally provided between the driving and driven pulleys to bias the V-belt with a spring, as disclosed in U.S. Pat. No. 3,643,518. The rotational speed variations of the V-belt are to be regulated in the manner that the tension pulley is moved against a bias force of the spring to suppress the increase of the tension when the tension of the V-belt is increased, and the tension pulley is urged in a spring restoring direction by the bias force of the spring to increase the tension when the tension of the V-belt is decreased.
In the abovementioned belt transmission device, conventionally, an efficiency of the transmissibility is regarded as so important that pulley groove angles of the driving or driven pulleys is limited in a range of 35.degree. to 40.degree., to get a high efficiency of belt transmission. This has great advantages if rotational speed variations of the engine do not occur. However, as mentioned above, in case the large rotational speed variations of the V-belt may occur, especially in a Diesel engine with an automatic speed-shifting gear, the abovementioned tension pulley must be employed.
Moreover, in a conventional device a supporting member for the tension pulley, a spring for biasing the tension pulley and the like must be employed in addition to the tension pulley in order to decrease the tension variations. Therefore, the cost is excessive due to a multiplicity of parts and the complexity of the arrangement.
Moreover, it is extremely disadvantageous to stow such a device in a small engine room of a motorcar, since the device is large-sized.